Formation of vertical devices by electroplating

ABSTRACT

The present invention is related to a method for forming vertical conductive structures by electroplating. Specifically, a template structure is first formed, which includes a substrate, a discrete metal contact pad located on the substrate surface, an inter-level dielectric (ILD) layer over both the discrete metal contact pad and the substrate, and a metal via structure extending through the ILD layer onto the discrete metal contact pad. Next, a vertical via is formed in the template structure, which extends through the ILD layer onto the discrete metal contact pad. A vertical conductive structure is then formed in the vertical via by electroplating, which is conducted by applying an electroplating current to the discrete metal contact pad through the metal via structure. Preferably, the template structure comprises multiple discrete metal contact pads, multiple metal via structures, and multiple vertical vias for formation of multiple vertical conductive structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/620,497, filed Jan. 5, 2007.

The present application is related to co-pending U.S. patentapplications entitled “MEMORY STORAGE DEVICES COMPRISING DIFFERENTFERROMAGNETIC MATERIAL LAYERS, AND METHODS OF MAKING AND USING THE SAME”(Attorney Docket No. YOR20060192US1-SSMP19771) and “FORMATION OFNANOSTRUCTURES COMPRISING COMPOSITIONALLY MODULATED FERROMAGNETIC LAYERSBY PULSED ECD” (Attorney Docket No. YOR20060194US1-SSMP19769), whichwere filed on even date herewith and are assigned to the same assigneeas the present application. The entire contents of such co-pending U.S.patent applications are incorporated herewith by reference for allpurposes.

BACKGROUND

The present invention relates to formation of vertical devices byelectroplating, and more specifically, to formation of verticalstructures using electroplating techniques.

Electroplating, which is also referred to as electrodeposition, has beenwidely used for metallization in semiconductor manufacturing.Electroplating is particularly useful for forming deep metal vias thatextend through the inter-level dielectric (ILD) layers to connect themetal contacts in different metal levels.

One of the conventional electroplating methods commonly used for coppermetallization in semiconductor manufacturing processes is referred to asthe damascene or superfilling method, as disclosed in U.S. Pat. No.6,709,562 entitled “METHOD OF MAKING ELECTROPLATED INTERCONNECTIONSTRUCTURES ON INTEGRATED CIRCUIT CHIPS” and illustrated herein by FIGS.1A-1C. First, a template structure is formed, which comprises asubstrate 100 and an inter-level dielectric (ILD) layer 101, as shown inFIG. 1A. The substrate 100 may be formed of either an insulator or asemiconductor with little or practically no conductivity. The ILD layer101 contains deep vias 102 therein, which can be readily formed bywell-known photolithography and etching techniques. Next, a continuousmetal seed layer 103 is deposited over the entire template structure, asshown in FIG. 1B. The metal seed layer 103 covers both the top surfaceof the ILD layer 101 and the sidewalls and bottom surfaces of the deepvias 102. The metal seed layer 103 comprises one or more contacts (notshown), through which an electroplating current can be applied to themetal seed layer 103. Electroplating of the template structure is thencarried out by using a special electroplating chemistry, whichpreferentially deposits metal 104 into the deep vias 102 of the ILDlayer 101 (i.e., the metal 104 is deposited into the deep vias 102 at arate that is significantly faster than on the top surface of the ILDlayer 101) to form metal wire structures free of voids, as shown in FIG.1C.

The above-described superfilling method has advantages in filling viaswith a single element or a homogeneous alloy of two or more differentelement. However, the superfilling method cannot be used to form acolumn with modulated compositions along a longitudinal axis thereof,due to several reasons. First, the electroplating step in this methodproceeds simultaneously on the bottom surface and over the sidewalls ofthe deep vias 102. Therefore, the superfilling method can only be usedto form compositionally homogeneous structures (i.e., structurescomprising the same metal or metal alloy throughout the entirestructures), but not compositionally modulated structures (i.e.,structures comprising alternating layers of different materialcompositions along the longitudinal direction). Further, thesuperfilling method requires a special electroplating chemistry, whichcontains numerous different additives, each of which exerts a differenteffect on the metal plating rate to jointly achieve the preferentialmetal deposition. Therefore, the superfilling method has so far onlybeen used for plating of a single metal, such as copper, but not forplating of metal alloys or alternating layers of different metals, dueto uncertainties related to how the different additives in the specialelectroplating chemistry will affect the plating rates of differentmetals.

Another conventional electroplating method, which is commonly used forforming metal wire structures, is referred to as the plating throughmask method and is illustrated by FIGS. 2A-2B. In this method, acontinuous metal seed layer 203 is firstly deposited over a surface ofthe substrate 200, followed by the deposition of an inter-level layer201 of photo-resist, dielectrics, or doped semiconductors withrelatively low conductivity over the metal seed layer 203. Next, deepvias 202 are formed in the inter-level layer 201 by photolithography andetching, as shown in FIG. 2A. During subsequent electroplating, anelectroplating current is applied to the metal seed layer 203 to deposita metal 204 over the bottom surfaces of the deep vias 202 and graduallyfill up the deep vias 202 to form vertical metal wire structures, asshown in FIG. 2B.

The plating through mask method is a bottom-up filling process, whichcan be used for forming not only metal wire structures that comprise asingle metal, but also those comprising metal alloys. Further, it can beused to form compositionally modulated structures comprising alternatinglayers of different material compositions along longitudinal axes of thestructures.

However, a major disadvantage of the traditional plating through mask orbottom-up plating process is the requirement for the continuous metalseed layer 203. Because the metal seed layer 203 is continuous over theentire surface of the substrate 200 and connects all the metal wirestructures, such metal wires cannot function independently of oneanother and therefore cannot be used to form separate electronicdevices, unless the metal seed layer 203 is selectively removed.However, because the metal seed layer 203 is sandwiched between theinter-level layer 201 and the substrate 200, it is almost impossible toremove it without disrupting or damaging the inter-level layer 201 andthe substrate 200.

There is a continuing need for an improved method for forming verticaldevice structures. More importantly, there is a need for an improvedmethod for forming separate vertical device structures that comprisealloys or alternating layers of different conductive materials.

BRIEF SUMMARY

The present invention employs discrete metal contact pads and metal viasfor applying the electroplating current during the electroplating step.Such discrete metal contact pads and metal vias remain parts of thefinal devices and therefore allow the formation of vertical conductivestructures that contain alloys of different conductive materials oralternating layers of different conductive materials, but withoutconnecting all the vertical conductive structures together or otherwiseaffecting the independent functionality of each vertical conductivestructures. In this manner, the resulting vertical conductive structurescan be readily used to form separate electronic devices.

In one aspect, the present invention relates to a method comprising:

forming a template structure comprising a substrate, a discrete metalcontact pad located over a top surface of the substrate, an inter-leveldielectric (ILD) layer covering both the substrate and the metal contactpad, and a metal via structure extending through the ILD layer(s) to thediscrete metal contact pad;

forming a vertical via in the template structure, wherein the verticalvia extends through the ILD layer onto the discrete metal contact pad;and

forming a vertical conductive structure in the vertical via byelectroplating,

wherein the electroplating is conducted by applying an electroplatingcurrent to the discrete metal contact pad under the ILD layer throughthe metallic via structure.

Preferably, but not necessarily, the vertical conductive structurecomprises one or more ferromagnetic metals. More preferably, thevertical conductive structure comprises alternating layers of differentferromagnetic metals. Alternatively, the vertical conductive structuremay comprise conductive polymers or doped semiconductor materials.

The template structure as described hereinabove may comprise a singlemetal contact pad on the upper surface of the substrate, with a singlemetal via structure and a single vertical via extending thereto forformation of a single vertical conductive structure. More preferably,the template structure of the present invention comprises multiplediscrete metal contact pads located on the upper surface of thesubstrate and having multiple metal via structures and multiple verticalvias extending thereto. In this manner, multiple vertical conductivestructures can be subsequently formed by electroplating in a singlewafer or chip, while the resulted vertical conductive structures are notinterconnected with one another.

In a specific embodiment of the present invention, the templatestructure further comprises a patterned metal layer that is located onan upper surface of the ILD layer and is electrically connected to allof the metal via structures, so that the electroplating can be carriedout by applying an electroplating current to the multiple discrete metalcontact pads through the patterned metal layer and the multiple metalvia structures.

The patterned metal layer is preferably formed before the vertical vias.More preferably, it is formed by first depositing a blanket metal layerover the ILD layer and then patterning the blanket metal layer to formmultiple openings that each is vertically aligned with one of themultiple discrete metal contact pads.

Further, an insulating layer can be formed over the patterned metallayer before formation of the multiple vertical vias, so that thesubsequently formed vertical vias extend through both the insulatinglayer and the ILD layer. More preferably, the patterned metal layer iscompletely covered by the insulating layer, except in the edge region ofthe processing unit, i.e., wafer or substrate, so that theelectroplating current can be carried through the edge region to thepatterned metal layer during subsequent electroplating. Afterelectroplating, both the patterned metal layer and the insulating layerare removed from the upper surface of the ILD layer, and multiplesurface metal contacts can be formed thereover to provide access to themultiple vertical conductive structures.

In another aspect, the present invention relates to a device structurethat comprises a substrate, a metal contact pad located over a topsurface of the substrate, an inter-level dielectric (ILD) layer coveringboth the substrate and the metal contact pad, a metal via structureextending through the ILD layer to the discrete metal contact pad, and avertical conductive structure extends through the ILD layer onto thediscrete metal contact pad.

Other aspects, features and advantages of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A-1C are cross-sectional views that illustrate the processingsteps of a conventional superfilling process for forming deep metalvias.

FIG. 2A-2B are cross-sectional views that illustrate the processingsteps of a conventional plating through mask process for forming deepmetal vias.

FIG. 3 is a cross-sectional view of two electronic devices, eachcomprising a functional unit, two auxiliary units, a metal contact padat each end of the functional unit, and a metal via structure extendingthrough the ILD layer to the metal contact pad that is located over anon-conductive substrate, according to one embodiment of the presentinvention. The metal via structures together with the metal contact padsprovide access to the functional units.

FIGS. 4-10 are cross-sectional views that illustrate exemplaryprocessing steps for forming the device structure of FIG. 3, accordingto one embodiment of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one skilled in the art that the invention may be practiced withoutthese specific details or by substituting certain details with knownequivalents thereof, without departing from the spirit of the invention.Further, standard structures or processing steps well known to thoseordinarily skilled in the art have not been described in detail in orderto avoid obscuring the invention.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present. It willalso be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

The term “vertical” as used herein refers to a structure or device thatis located over a substrate surface, and the longitudinal axis of such astructure or device is perpendicular to the substrate surface.

The term “metal contact” or “metal contacts” as used herein refers tometal structures of limited lateral extension. Unlike a continuous metallayer that covers the entire substrate surface or a majority portionthereof, the metal contact or metal contacts only extend(s) over aselected region or selected regions of the substrate surface upon whichsubsequent device structures are to be built. The metal contact or metalcontacts can be formed by patterning a continuous metal layer.

The term “discrete” as used herein refers to structures that areisolated from each other with no overlap therebetween.

The term “ferromagnetic material” as used herein refers to any materialthat can be magnetized by applying an external magnetic field andexhibits remnant magnetization after the external magnetic field isremoved.

As mentioned hereinabove, the present invention uses discrete metalcontact pads and metal via structures, which are the existing elementsof an integrated circuit, to apply electroplating current duringelectroplating for forming vertical conductive structures. The resultingvertical conductive structures preferably, but not necessarily, containalloys of different conductive materials (i.e., metals, conductivepolymers, or doped semiconductors) or alternating layers of differentconductive materials. The present invention is particularly useful forforming ferromagnetic structures that comprise alternating ferromagneticlayers of different material compositions, as described by theco-pending U.S. patent applications entitled “MEMORY STORAGE DEVICESCOMPRISING DIFFERENT FERROMAGNETIC MATERIAL LAYERS, AND METHODS OFMAKING AND USING THE SAME” (Attorney Docket No.YOR20060192US1-SSMP19771) and “FORMATION OF NANOSTRUCTURES COMPRISINGCOMPOSITIONALLY MODULATED FERROMAGNETIC LAYERS BY PULSED ECD” (AttorneyDocket No. YOR20060194US1-SSMP19769). However, applications of thepresent invention are not limited to ferromagnetic structures, butextend broadly to cover any device structure that requires verticalconductive structures.

FIG. 3 shows a cross-sectional view of a device structure containing twogeneral electronic devices with vertical conductive structures 305. Eachof the electronic devices may include: (1) a vertical functional unit,i.e., the vertical conductive structure 305, (2) conductive contacts 302and 304 at both ends of the functional unit 305, (3) a metal via 303that extends onto the bottom conductive contact 302 to provide access tothe bottom conductive contact 302, and (4) certain auxiliary elementsand associated circuits 306. The auxiliary elements and circuits 306 canbe either reading and writing elements or other sensing and controllingelements for the functional unit 305.

The device structure as described hereinabove is formed over anon-conductive substrate 300 with an ILD layer 301 located thereover.The non-conductive substrate 300 may comprise any suitablenon-conductive material, and it preferably comprises a ceramic,dielectric, glass or polymer material, including, but not limited to:Al₂O₃, SiO₂, Si₃N₄, and HfO₂. Further, the non-conductive substrate 300may comprise an un-doped or lowly doped semiconductor material,including, but not limited to: Si, SiC, SiGe, SiGeC, Ge alloys, GaAs,InAs, InP, as well as other III-V or II-VI compound semiconductors. TheILD layer 301 may be formed of any suitable photoresist or dielectricmaterial, such as, for example, SiO₂, Si₃N₄, HfO₂, and Al₂O₃.

The device structure of FIG. 3 can be formed by exemplary processingsteps as illustrated by FIGS. 4-10, according to one embodiment of thepresent invention.

FIG. 4 shows a template structure that comprises the non-conductivesubstrate 300, the ILD layer 301, the bottom metal contacts 302, themetal vias 303, and the auxiliary elements 306 (optional). Such atemplate structure can be readily formed by conventional semiconductorprocessing and metallization techniques, which are not described here inorder to avoid obscuring the present invention.

Next, as shown in FIG. 5, a patterned metal layer 404 is deposited overa top surface of the ILD layer 301. The patterned metal layer 404 formsan electrical contact with all the metal vias 303, and through suchmetal vias 303, the patterned metal layer 404 forms electrical contactwith all the bottom metal contacts 302. The patterned metal layer 404can be readily formed by first depositing a blanket metal layer (notshown) over the entire top surface of the ILD layer 301, followed bypatterning the blanket metal layer (not shown) to form multiple openings405. Each of the openings 405 in the patterned metal layer 404 isvertically aligned with one of the bottom metal contacts 302, therebydefining the locations where the vertical conductive structures 305 areto be formed. Patterning of the blanket metal layer (not shown) can bereadily carried out using any conventional metal patterning techniques,such as lithography, etch back, lift-off, etc.

As shown in FIG. 6, a layer of insulating material 406 is then depositedover the patterned metal layer 404 to cover the entire layer 404 exceptat the edge region 407. The insulating material layer 406 can be formedof the same insulating material as the ILD layer 301, but generally itis formed of a different insulating material. In the semiconductormanufacturing process, numerous devices are fabricated simultaneously onthe same wafer. Therefore, the edge region 407 denotes the edge regionof the wafer. In this manner, the patterned metal layer 404 can still beaccessed at the edge region 407 after formation of the insulatingmaterial layer 406, which the patterned metal layer 404 in turn providesaccess to the bottom metal contacts 302 through the metal vias 303.

Subsequently, as shown in FIG. 7, a patterning process (preferably anetching process, such as reactive ion etching) is carried out to formvertical vias (or deep vias) 408 through the insulating layer 406 andthe ILD layer 301. The dimension and shape of the vertical vias 408define the dimension and shape of the vertical conductive structures 305to be formed. The vertical vias 408 can be of any size or shape,depending on the requirements for the final devices and the limitationsof the fabrication process. Preferably, each of the vertical vias 408 soformed has a depth ranging from about 1 micron to about 1000 microns anda cross-sectional diameter ranging from about 10 nm to about 1000 nm.The vertical vias 408 can have any suitable cross-sectional shape,including, but not limited to: circular, square, rectangular,triangular, polygonal, semi-circular, elliptical, ring-shaped, etc.Depending on whether the insulating layer 406 and the ILD layer 301comprise the same or different insulating material(s), the etchingprocess may comprise either a single etching step or multiple etchingsteps.

After the etching, electroplating is carried out by first immersing theabove-described structure in an electroplating solution and thenapplying an electroplating current to the patterned metal layer 404 bycontacting the edge region 407. In this manner, the electroplatingcurrent is carried through the patterned metal layer 404 and the metalvias 303 to the discrete metal contact pads 302 at the bottom surface ofthe ILD layer 301, so that a conductive material 305 is deposited ontothe discrete metal contact pads 302 and gradually fills the verticalvias 408 in a bottom-up manner. The electroplating solution as describedhereinabove may comprise a single salt for deposition of a singleelemental, or salts of different elements for deposition of an alloy.The resulted structure 305 can comprise any suitable conductivematerials, such as metals, doped semiconductors, conductive polymers,and alloys thereof, but it preferentially comprises a metal or metalalloy. Electrodeposition of metals, doped semiconductors, and conductivepolymers is well known in the art and is therefore not described indetail herein.

Preferably, but not necessarily, the electroplating solution comprisessalts of two or more different ferromagnetic metals for deposition of aferromagnetic metal alloy. More preferably, the electroplating can becarried out by applying a pulsed electroplating current with high andlow potential pulses for deposition of alternating ferromagnetic layersof different material compositions, as described in the co-pending U.S.patent application entitled “FORMATION OF NANOSTRUCTURES COMPRISINGCOMPOSITIONALLY MODULATED FERROMAGNETIC LAYERS BY PULSED ECD” (AttorneyDocket No. YOR20060194US1-SSMP19769).

The electroplating step is allowed to proceed until the vertical vias408 are completely filled with the metal to form vertical conductivestructures 305, as shown in FIG. 8. The dimension and shape of thevertical conductive structures 305 are defined by the vertical vias 408.Therefore, the vertical conductive structures 305 may also have a depthranging from about 1 micron to about 1000 microns and a cross-sectionaldiameter ranging from about 10 nm to about 1000 nm, and they may alsohave any suitable cross-sectional shape, including, but not limited to:circular, square, rectangular, triangular, polygonal, semi-circular,elliptical, ring-shaped, etc.

After the electroplating, multiple etching and/or polishing steps can becarried out to remove the overgrown portions of the vertical conductivestructures 305, the insulating layer 406, and the patterned metal layer404, and to planarize the again-exposed upper surface of the ILD layer301 with the metal via 303 and the newly formed vertical conductivestructure 305, as shown in FIG. 9.

Next, a patterned insulating layer 410 is deposited over the exposedupper surface of the ILD layer 301, as shown in FIG. 10. The patternedinsulating layer 410 may comprise either the same or different materialfrom that of the ILD layer 301, and it contains multiple openings 411,through which the vertical conductive structures 305 and the metal vias303 are exposed. In this manner, surface metal contacts 304 can beformed in the openings 411 to provide access to the vertical conductivestructures 305 and the metal vias 303, thereby forming a complete devicestructure as shown in FIG. 3.

Note that while FIGS. 3-10 illustratively demonstrate exemplary devicestructures and processing steps according to specific embodiments of thepresent invention, it is clear that a person ordinarily skilled in theart can readily modify such device structures and processing steps foradaptation to specific application requirements, consistent with theabove descriptions. For example, although the exemplary devicestructures as shown in FIGS. 3-10 each contain a single ILD layer, twodiscrete metal contact pads and two vertical conductive structures, itis readily understood that the device structure of the present inventionmay comprise any numbers of ILD layers, discrete metal contact pads, andvertical conductive structures. Further, the device substrates of thepresent invention can be readily used for forming any semiconductordevices that require vertical conductive structures with at least onebottom metal contacts.

While the invention has been described herein with reference to specificembodiments, features and aspects, it will be recognized that theinvention is not thus limited, but rather extends in utility to othermodifications, variations, applications, and embodiments, andaccordingly all such other modifications, variations, applications, andembodiments are to be regarded as being within the spirit and scope ofthe invention.

1. A device structure comprising a substrate, a discrete metal contactpad located over a top surface of said substrate, an inter-leveldielectric (ILD) layer covering both the substrate and the at least onemetal contact pad, a metal via structure extending through the ILD layeronto the discrete metal contact pad, and a vertical conductive structureextending through the ILD layer onto the discrete metal contact pad. 2.The device structure of claim 1, wherein the vertical conductivestructure comprises one or more ferromagnetic metals.
 3. The devicestructure of claim 2, wherein the vertical conductive structurecomprises alternating layers of different ferromagnetic metals.
 4. Thedevice structure of claim 1, comprising multiple discrete metal contactpads, each of which has a metal via structure and a vertical conductivestructure extending thereto.
 5. The device structure of claim 4, furthercomprising multiple surface metal contacts located over an upper surfaceof the ILD layer, wherein each of the multiple surface metal contacts iselectrically connected with one of the multiple vertical conductivestructures.